The present invention relates to a gel method of printing variable information, more particularly to a printing method involving a special ink, which is gelled by means of an energy source.
In recent years, copying and printing technologies have begun to merge. Copying may be described as the ability to reproduce an original document one or more times. Printing may be described as creating a master that can be used to produce multiple impressions. Both processes create multiple copies of identical information.
For many years, copying has been dominated by electro-photography and more specifically xerography. An important means of printing that has been strongest in the market for printing impressions onto paper is offset lithography. Development and wide distribution of computers has enabled origination for printing to be prepared in an electronic form. While the need to copy documents is still widespread, documents can also be generated directly from computers using similar electrophotographic techniques as those that were originally developed for document copying. Similarly, printing plates can be produced directly from computers and used on offset lithographic machines for multiple impressions. These two types of processes have become opposite economic ends of the printing process, with electrophotographic printing being most economical for short runs and offset lithography being most economic for long runs. Each process has its own advantages and disadvantages. Although xerographic printing has a great complexity of technology, it has the ability to vary information from print to print, whereas offset has a fixed master.
Two of the big disadvantages of electro-photography are the need to use a toner and the limits of the speed of the process due to its complexity. The toner, which is particulate in structure, is relatively expensive to produce and has a limit to the minimum size of particles, which also affects quality of reproduction.
Electrocoagulation is a process described by Castegnier, in an article entitled xe2x80x9cOptimizing the Electrography Printing Cycle (ISandT""s NIP13: 1997 International Conference on Digital Printing Technologies, p.746). Imaging is accomplished by an array of electrodes which, when current flows, cause ink to coagulate and gel. As described in the article, the system adjustment is very critical. Also, current flows from electrode tips and it is difficult to direct it in an accurate manner, because it can flow from any point on the surface of the electrode, resulting in poor image quality.
Other processes such as ink jet are also being used for printing, aimed at providing fast variable printing. However, the ink jet process has difficulty printing good quality color work on a variety of printing stock. The present invention seeks to overcome these and other disadvantages.
It would be desirable to provide a printing method which uses an ink and not a toner, which is capable of producing variable information from print to print, which has simpler stages than those of electro-photography and which can be printed onto a large variety of printing stocks.
In accordance with a preferred embodiment of the present invention there is provided a method of printing on media, comprising the steps of:
applying a radiation sensitive ink to a surface of a cylinder;
radiating energy in an image pattern so as to create image and non-image areas, such that said ink in said image areas becomes gelled and said ink in said non-image areas does not gel;
wiping said non-gelled ink away from said surface of said cylinder; and
transferring said gelled ink onto the media.
The method of the invention involves special inks that are applied onto a substrate that is part of or attached to a cylinder of the printing machine. Imaging is by means of an energy source in the UV, visible or infrared regions, modulated to represent a digital image pattern that has been composed on a computer.
The consequence of imaging is to gel the ink and increase its adhesion to the substrate of the printing cylinder. The non-gelled background ink with lower adhesion is then removed by a squeegee action and returned to an ink reservoir. The remaining image is transferred to an offset blanket or directly to print stock by pressure. The cycle may or may not continue with a brief cleaning of the cylinder surface before recoating for the next cycle and the next print. The ink that is transferred to the print stock can be further dried, either by the same type of radiation that resulted in gelation during imaging, or by another form of radiation.
It is possible to configure a machine in a similar manner to a laser printer in that all of the steps happen in one rotation of the drum of the machine. This means that all of the stages as described below will occur simultaneously. This would be done in order that the process be suitable for printing each print from its own digital filexe2x80x94i.e. variable information. Thus, the process does not use a master, but produces an image that is erased after printing with each cylinder rotation, so that the next rotation producing the next print can have fresh information written upon it.